Dealing with Combined Sewer Overflows

According to the U.S. Environmental Protection Agency (EPA), combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers or other water bodies.

Combined sewer overflows (CSOs) collect everything from road dust, tire debris, leaking gas, oil, diesel, road salts and any spilled chemicals. Moreover, the gutter downspouts wash the pollutants that have settled on the roofs of buildings into the combined sewers.

Seventeen municipal wastewater systems in Kentucky have combined sewers and permitted CSOs. These “CSO communities” have entered into consent agreements with the Department for Environmental Protection or jointly with the DEP and the U.S. Environmental Protection Agency (EPA) to manage or eliminate CSOs in their wastewater collection systems.  The communities are located across Kentucky and range in size from the state’s largest sewer utility, Louisville & Jefferson County’s Metropolitan Sewer District, to the city of Loyall in Harlan County, which serves a population of 700.  The first of the CSO communities to eliminate their CSOs was Pikeville, which completed the separation of the storm sewers from the sanitary system in 2014.

In order to manage their CSOs, the Kentucky communities have committed to complete construction projects, which will total in the billions of dollars. Because the majority of those costs will be passed on to the utilities’ customers, affordability is a key consideration in determining the time required for completion of the CSO control programs. The EPA’s CSO control policy includes provisions for determining the financial burden on the customer base, and provides for extensions of time for completion of projects in cases of high burden. However, the CSO communities must demonstrate whether their sewer rates meet the high burden category.  Although the completion dates are not set in all cases, the remaining sixteen CSO communities are working on projects, which will result in the management or elimination of their combined sewer overflows and result in improvements in water quality across Kentucky.

This figure shows representations of combined sewers and separate sewers

This figure shows representations of combined sewers and separate sewers

A new study from Chicago-based researchers has found that a confluence of sewage overflows and widespread antibiotic use is causing the proliferation of antibiotic-resistant bacteria in waterways around the Windy City. To view the complete article, click on the following link.

Antibiotics Driving Resistant Bacteria In Urban Sewers

This is one study looking at only one chemical and its effect in one urban area. In the water and wastewater industry, we know that there are pollutants (about 2,000 new ones each year) that affect organisms, but we don’t know at what level these pollutants have an effect. Is it at parts per million, billion or trillion? That has yet to be determined.

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